Field of the Invention
The present invention relates to membrane switches which have a sheet-like shape. The present invention also relates to various uses of such a membrane switch.
Discussion of the Background
A membrane switch is a sheet-like switch wherein a conductive part (part made of an electrically conductive material to be a contact of the switch) is formed on each of two sheets of substrates, and the substrates are laminated with a spacer lying between them such that the conductive parts face each other and a space is secured between the conductive parts (see JP-A-01-076625, which is incorporated herein by reference in its entirety).
FIGS. 10A and 10B are cross-sectional views schematically showing an enlarged structure of one switch part of a conventional membrane switch. As shown in these Figures, conductive parts 110, 210 to be contact points are formed on each of two sheets of substrates 100, 200, and a spacer 300 is interposed between them such that the conductive parts 110, 210 face each other with a predetermined space s therebetween.
In the embodiment of FIG. 10A, since the area of conductive parts 110, 210 is larger than the opening area of a through-hole 310 formed in the spacer 300, the outer-peripheral edges of the conductive parts 110, 210 protrude from the opening of the through-hole in the spacer. In FIG. 10A, although the conductive parts are drawn to appear thick for explanation, they are in fact thin and the spacer is not highly compressed by the conductive parts during assembly. On the other hand, in the embodiment of FIG. 10B, since the area of conductive parts 110, 210 is smaller than the opening area of a through-hole 310 formed in the spacer 300, the conductive parts 110, 210 face each other while being settled in the opening of the through-hole in the spacer.
In a membrane switch, at least one of the opposing conductive parts 110, 210 is movable (capable of being displaced toward the other conductive part, making contact therewith and returning) due to the elasticity of the substrate. Therefore, as shown with thick arrows in FIGS. 10A and 10B, when a substrate on the movable conductive part side is pressed from the outside, two conductive parts 110, 210 come into contact to be electrically conducted, and when pressing is released, contacting is broken and on and off signals can be obtained.
Since such a membrane switch has a simple structure, it can be manufactured at a low cost and the reliability of an on-off operation is high, it is frequently utilized in a wide range of fields for a keyboard of a mobile phone or a personal computer, switches of household electrical appliance, switches of remote-controller and the like.
The present inventors detailedly studied the structure and function of the conventional membrane switch as mentioned above, and took note of the fact that conventional membrane switch is simply capable of receiving only on (close) and off (open) signals. They took up a problem that the use thereof should be expanded more than not only on and off, by imparting a membrane switch with a new structure capable of outputting a signal corresponding to the amount of the pressure applied from the outside.